The present invention generally relates to novel polymers and methods of making the same.
Molecular weight distribution (MWD), or polydispersity, is a well known variable in polymers. The molecular weight distribution can be measured directly, e.g., by gel permeation chromatography (GPC) techniques, or indirectly, by measuring I10/I2 ratio, as described in ASTM D-1228. The polydispersity or polydispersity index (PDI), defined as the ratio of the weight average moelcular weight (Mw) to the number average molecular weight (Mn) (i.e., Mw/Mn), is a single index of the breadth of the MWD. The larger the PDI, the broader the MWD.
Fluoropolymers, such as for example, homo, co, and terpolymers of vinylidene fluoride, have been observed to exhibit excellent physical properties including resistance to weathering, UV, and chemicals. Accordingly, these materials are well-suited for a number of applications relating to high temperature wire insulation, chemical tank linings, protecting paints and coatings, valves and impeller parts, and sealants. Notwithstanding these advantages, these fluoropolymers often possess low melt elasticity causing problems in melt fabrication. Additionally, such polymers may experience melt fracture surface properties at relatively low extrusion rates thereby processing in a less than desirable manner. Low shear sensitivity (i.e., a low I10/I2 value) often limits the extrudability of such polymers.
There is a need in the art to address the above-mentioned problems with respect to fluoropolymers.
In one aspect, the invention provides a method for forming a fluoropolymer. The method comprises providing a reaction mixture comprising carbon dioxide, at least one fluoromonomer, and an initiator; and reacting the at least one fluoromonomer in the reaction mixture to form a fluoropolymer. The fluoropolymer has a multimodal molecular weight distribution.
In another aspect, the invention provides a fluoropolymer having a multimodal molecular weight distribution. The fluoropolymer has a weight average molecular weight to number average molecular weight ratio of from about 2 to about 10.
In another aspect, the invention provides a composition of matter. The composition of matter comprises a mixture comprising carbon dioxide and a fluoropolymer having a multimodal molecular weight distribution. The fluoropolymer has a weight average molecular weight to number average molecular weight ratio of from about 2 to about 10.
Other aspects of the present invention are presented in detail in the specification set forth below.